Japanese Patent Publication (KOKOKU) No. 60-1404(1985) discloses highly crimpable conjugated fibers, produced by the conjugate spinning of a block polyester polyether and a nonelastic polyester consisting essentially of polybutylene terephthalate into a side-by-side type or an concentric sheath-core type and suitably usable as outer garments or underwear as conjugated fibers comprising a crystalline thermoplastic elastomer and a crystalline thermoplastic polyester. Japanese Laid-Open Patent Publication No. 3-185116(1991) discloses highly crimpable heat-bonding conjugated fibers, produced by the conjugate spinning of a polyester ether elastomer and a nonelastic polyester consisting essentially of polyethylene terephthalate into the side-by-side type or sheath-core type, readily openable by a carding engine and suitable for producing nonwoven fabrics with stretchability. Japanese Laid-Open Patent Publication No. 3-220316(1991) describes substantially concentric sheath-core type heat-bonding conjugated fibers having a polyester elastomer arranged as a sheath component and a nonelastic polyester arranged as a core component, improved in carding performance and spinning properties and useful for producing spun yarns and heat-bonding nonwoven fabrics. Furthermore, International Application Published under the Patent Cooperation Treaty WO91/19032, Japanese Laid-Open Patent Publication Nos. 4-240219(1992), 4-316629(1992), 5-98516(1993), 5-163654(1993), 5-177065(1993), 5-261184(1993), 5-302255(1993), 5-321033(1993), 5-337258(1993), 6-272111(1994), 6-306708(1994) and the like disclose heat-bonding conjugated fibers having a thermoplastic elastomer arranged on the fiber surfaces and further fiber structures obtained by using the same.
The cross sections of the various heat-bonding conjugated fibers disclosed in the prior art set forth above are literally the side-by-side type and eccentric sheath-core type as shown in FIGS. 2(a) to 2(c). In these cases, the thermoplastic elastomer and nonelastic polyester are joined at an area ratio within the range of (20/80) to (80/20). By the way, in conjugated fibers using an elastomer as one component, a cohesion phenomenon of mutual conjugated fibers inevitably occurs due to the properties of the elastomer in the spinning step or thereafter causing various problems to occur. In this sense, none of the prior art with describe techniques for obtaining conjugated fibers with improved adhesion, elasticity and crimpability while overcoming the cohesion phenomenon of mutual fibers nor suggest even the recognition thereof. Japanese Laid-Open Patent Publication No. 5-302255(1993) discloses, without regard to the presence of the recognition described above, the conjugate spinning of an elastomer, containing a large amount of a polyether component, with excellent elastic characteristics in spite of great cohesion properties and arranged as a core component and an elastomer, containing a small amount of the polyether component, with poor elastic characteristics in spite of slight cohesion properties as a sheath component in mutual conjugate spinning of polyester elastomers having different compositions into the sheath-core type and obtaining continuous filaments. However, preventing effects of cohesion at a practical level have not been obtained in conjugated fibers. Furthermore, conjugated fibers have uses of materials for nonwoven fabrics useful as cataplasma materials, interlining cloths, supporters, stretchable tapes and the like. Further, Table 1 shows the results of considerations for overall performance, i.e. the ability to prevent cohesion, interfacial adhesive strength between elastomer/polyester polymer, essential heat-bonding properties and crimp modulus of conventional heat-bonding conjugated fibers illustrated in FIGS. 2(a) to 2(c).
TABLE 1 __________________________________________________________________________ Conjugated Fiber (a) Conjugated Fiber (b) Conjugated Fiber (c) __________________________________________________________________________ Fiber Manufacturing Property 1) Housing property of Good Bad Bad undrawn yarn in subtow can in spinning 2) Yarn breakage in Slight Many Many drawing 3) Discharge property Good Bad Bad of stuffing crimper Characteristics of Conjugated Fiber 4) Ability to prevent Great Small Small cohesion in spinning 5) Adhesive strength Low High High between elastomer/ (High)* polyester (polymer interface) 6) Thermal adhesive strength among filaments (No cohesion)** (Low)** (High)** (High)** *Cohesion Low Low Low 7) Crimp modulus of Low High High elasticity 8) Three-dimensional Great None Great crimpability 9) Opening property Bad Bad Bad in opening step Opening and Carding Performance 10) Wrapping around Bad Bad Bad card cylinder 11) Unevenness of card Bad Bad Bad web 12) Card nep Bad Bad Bad Characteristics of Fiber Structure 13) Compression resilience Low Low Low after heat treatment (Due to low (Binder characteristics (Binder characteristics thermal adhesive cannot be manifested cannot be manifested strength) due to great cohesion due to great cohesion in spite of high in spite of high thermal adhesive strength) thermal adhesive strength) 14) Hardness unevenness Great Great Great after heat treatment (Great unevenness (Great unevenness (Great unevenness of hardness due to of hardness due to of hardness due to great unevenness of web) great unevenness of web) great unevenness of web) 15) Compression Small Small Small durability after heat treatment __________________________________________________________________________
Table 1 shows the results of a relative evaluation based on conjugated fibers (b), and "*)" in the table indicates a polyester elastomer. "**)" indicates an imaginary case in which of no cohesion occurs. As can be seen from tree results in Table 1, conjugated fibers (c) are excellent in 4 requirements of 5 prescribed properties corresponding to 4) to 8) in the table!, and they are considered as ideal fibers at a glance. However, "small", i.e. poor ability to prevent cohesion of the single filaments produces fatal disadvantages in the industrial production process or in the resulting products as described hereinafter. That is, the conjugated fibers are initially collected as undrawn yarns by winders or subtow cans. The following problems arise: Insufficient cooling causes cohesion due to the elastomer at the time of bundling mutual single filaments. However, even in a state of the undrawn yarns wound on winders and stored, there are problems in that mutual cohesion of the single filaments proceeds to become a hard stringy form and subtows mutually firmly adhere and cannot be unwound from the winders. Even when the undrawn yarns are collected in subtow cans, there are problems in remarkably reduced amounts of the undrawn yarns housed in the subtow cans and a marked reduction in productivity due to the cohesion thereof into a stringy hard state. As mentioned above, subtows sticking together into the stringy form are extremely poor in drawability in the drawing step and yarn breakage or wrapping around roll stand units frequently occurs. Therefore, stable production cannot be performed. Even if heat-bonding fibers can be produced, the mutual fibers stick together as a mass. Because of this, the number of formed heat-bonded spots effective for bonding the mutual fibers is small in heat treatment in forming the fibers into a fiber structure such as a nonwoven fabric or the like and mixing thereof with other matrix fibers for use. Therefore, there are problems in that the adhesion is markedly low without any elasticity and the fiber structure is readily destroyed by external force with durability being lost. On the other hand, the ability of the conjugated fibers (a) to prevent cohesion is doubled as compared with that of conjugated fibers (b) or (c). The conjugated fibers (a), however, have problems of marked deterioration in heat-bonding functions and crimp modulus which are essential objects.